supagridIn the NEM, electricity is not traded by company name or power station name. It is traded through individual market units, each of which represents a specific physical asset connected to the grid.
Understanding the difference between generators, units, and identifiers is essential for interpreting dispatch, pricing, and performance data correctly.
Generators vs Power Stations
In everyday language, a generator often refers to a power station. In the NEM, this distinction matters.
A power station:
- Is a physical site
- May contain one or more generating machines
- Is often owned by a single participant
In market terms, a power station is typically made up of multiple units, each of which participates in dispatch independently.
What Is a Unit
A unit is the fundamental building block of the NEM market.
Each unit:
- Represents a single dispatchable asset
- Submits its own bids
- Receives its own dispatch targets
- Is constrained independently
A large coal station, for example, may consist of multiple units, each with its own operating limits and bidding behaviour.
Dispatch occurs at the unit level, not at the power station level.
Dispatchable vs Non-Dispatchable Units
Not all units behave the same way in the market.
Dispatchable units:
- Can control their output
- Submit price and quantity bids
- Receive explicit dispatch targets
Non-dispatchable units:
- Are driven by availability, such as wind or solar
- Do not bid in the same way
- Are dispatched based on forecast output and system conditions
Both types of units influence prices and system behaviour, but they do so in different ways.
DUIDs
Each unit in the NEM is identified by a Dispatchable Unit Identifier, commonly referred to as a DUID.
A DUID:
- Uniquely identifies a unit in the market
- Is used in dispatch, pricing, and settlement
- Appears consistently across NEM datasets
DUIDs are the primary key for most market data. Understanding them is critical when analysing historical outcomes or real-time behaviour.
Most NEM data is indexed by DUID, not by company or station name.
Why One Station Has Multiple DUIDs
Many power stations have multiple DUIDs because each unit is treated as a separate participant in the dispatch process.
This allows the market to:
- Dispatch units independently
- Reflect different technical capabilities
- Capture maintenance or outage impacts at a granular level
As a result, analysing performance at the station level usually requires aggregating multiple units.
Unit Capabilities and Limits
Each unit has defined technical limits that constrain how it can operate.
These include:
- Maximum and minimum output
- Ramp rates
- Availability limits
- Start-up and shutdown characteristics
These limits are enforced by the market and can affect whether a unit is dispatched, even if it is competitively priced.
Ownership and Participation
Units are registered to market participants, typically generation companies. A single participant may own many units across different regions and technologies.
Ownership does not affect dispatch directly. Units compete based on their bids and technical limits, not who owns them.
Why This Matters
Misunderstanding units and DUIDs can lead to incorrect conclusions about market behaviour.
This concept explains:
- Why output differs across units at the same station
- Why some assets appear constrained while others are not
- Why aggregation choices matter in analysis
- Why bids and prices must be interpreted at the unit level
What to Take Away
The key ideas to remember are:
- Units are the core market participants
- Dispatch happens at the unit level
- DUIDs uniquely identify units
- Stations often consist of multiple units
With this foundation, it becomes much easier to understand dispatch behaviour and price formation.
Continue with Dispatch & Pricing to see how units are dispatched and how prices are set.